Forged iron-type golf clubs

ABSTRACT

Forged cavity back iron-type clubs and oversize clubs are disclosed. These forged clubs have thin, durable hitting face and relatively large cavity volumes. These clubs have high rotational moments of inertia to minimize distance and accuracy penalties associated with off-center hits. Long irons with hitting face of about 0.100 inch thick are achievable by the present invention. Also disclosed are forged irons made from stainless steels and annealed to achieve the desired hardness and ductility.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending U.S. application Ser. No.10/640,537, which was filed Aug. 13, 2003.

FIELD OF THE INVENTION

This invention generally relates to golf clubs, and, more particularly,to iron-type clubs.

BACKGROUND OF THE INVENTION

Individual iron club heads in a set typically increase progressively inface surface area and weight as the clubs progress from the long ironsto the short irons and wedges. Therefore, the club heads of the longirons have a smaller face surface area than the short irons and aretypically more difficult for the average golfer to hit consistentlywell. For conventional club heads, this arises at least in part due tothe smaller sweet spot of the corresponding smaller face surface area.

To help the average golfer consistently hit the sweet spot of a clubhead, many golf clubs are available with cavity back constructions forincreased perimeter weighting. Perimeter weighting also provide the clubhead with higher rotational moment of inertia about its center ofgravity. Club heads with higher moment of inertia have a lower tendencyto rotate caused by off-center hits. Another recent trend has been toincrease the overall size of the club heads, especially in the longirons. Each of these features increases the size of the sweet spot, andtherefore makes it more likely that a shot hit slightly off-center stillmakes contact with the sweet spot and flies farther and straighter. Onechallenge for the golf club designer when maximizing the size of theclub head is to maintain a desirable and effective overall weight of thegolf club. For example, if the club head of a three iron is increased insize and weight, the club may become more difficult for the averagegolfer to swing properly.

In general, the center of gravity of these clubs is moved toward thebottom and back of the club head. This permits an average golfer to getthe ball up in the air faster and hit the ball farther. In addition, themoment of inertia of the club head is increased to minimize the distanceand accuracy penalties associated with off-center hits. In order to movethe weight down and back without increasing the overall weight of theclub head, material or mass is taken from one area of the club head andmoved to another. One solution has been to take material from the faceof the club, creating a thin club face. Examples of this type ofarrangement can be found in U.S. Pat. Nos. 4,928,972, 5,967,903 and6,045,456.

Iron-type clubs, which include wedge clubs, are typically made byinvestment casting, machining or forging. Forged club heads are covetedby the higher skilled amateur golfers and professionals for its superiorplaying characteristics. On the other hand, forgeable alloys aremalleable and typically have low yield strengths. For forged clubs, theface of the club cannot heretofore be made thin, because of thisdrawback.

Commercially available forged iron-type clubs are typically the muscleback type, such as the Titleist® Forged 670, 680 and 690 series,Mizuno's MP-33 irons and Kenneth Smith's Royal Signet clubs. The RoyalSignet® muscle back clubs concentrate the club weight near the centersweet spot, thereby reducing its moment of inertia. Forged cavity backiron-type clubs are also available, as midsize clubs with relativelythicker hitting face, such as the Titleist® 690-CB, the Hogan Apex EdgePro or the Royal Signet® Titanium. The Hogan Apex Edge Pro irons aresingle-piece clubs forged from carbon steel, but the Hogan CFT clubshave a stamped titanium face in a cast body. The Royal Signet® Titaniumclubs are cast stainless steel clubs with a forged titanium full faceinsert for additional strength.

Hence, a need still exists for improved forged iron-type golf clubs.

SUMMARY OF THE INVENTION

Hence, the invention is directed to forged golf clubs.

The present invention is directed to golf clubs wherein the entire clubhead is forged from metal ingot.

The present invention is also directed to forged iron-type golf clubs.

The present invention is further directed to oversize forged iron-typeclubs.

The invention is also directed to an iron-type golf club comprising aclub head having a hosel, a front and a back, wherein the back comprisesa cavity defined by a perimeter member and the front has a hitting zonelocated opposite to and coinciding with the cavity. The club head isforged from a malleable metal, such as stainless steel, and thenpreferably annealed. The cavity and the substantially flat front faceform a hitting zone having a first portion and a thicker reinforcedportion. The reinforced portion is preferably located below the firstportion and may have one or more depressions defined therein. Thethickness of the reinforced portion is about 1.2 times to about 3 timeshigher than the thickness of the first portion.

The first portion occupies from about 50% to about 90% of the total areaof the hitting zone, and more preferably from about 60% to about 80% ofthe total area of the hitting zone. The perimeter member is preferablythicker on the bottom of the club head than on the top.

The present invention is also directed to an iron-type golf clubcomprising a club head made from single-piece or multiple-piece forgedstainless steel. The club head comprises a hosel, a front and a backdefining a cavity, and the front comprises a hitting zone locatedopposite to the cavity and is defined by the cavity area. The cavity hasa volume equal to or greater than about 10 cc. A set of inventive ironshas cavity volumes defined as greater than or equal to curve A in FIG.11. More preferably the cavity volume through a set is greater than orequal to curve B in FIG. 11. Preferably, the forged stainless steel isannealed after forging.

The present invention is further directed to an iron-type golf clubcomprising a club head made from forged metal, said club head comprisesa hosel, a front and a back defining a cavity, wherein the frontcomprises a hitting zone located opposite to and coinciding with thecavity and wherein the hitting zone has an area equal to or greater thanabout 2.25 inch² and the cavity has a volume equal to or greater thanabout 9 cc. A preferred set of such irons has an average hitting zoneequal to or greater than about 2.25 inch² and average cavity volumeequal to or greater than about 9 cc. More preferably, the hitting zoneis equal to or greater than about 2.4 inch² and average cavity volumeequal to or greater than about 12 cc.

The present invention is further directed to an iron-type golf clubcomprising a club head made from forged metal, said club head comprisesa front face and a back defining a cavity, wherein the front facecomprises a hitting zone opposite to the cavity and the hitting zone hasa minimum thickness less than about 0.2 inch for the set. Morepreferably, the thickness is less than about 0.13 inch for clubs havingloft angles (LA) less than about 30°.

The present invention is further directed to an iron-type golf clubcomprising a club head made from forged metal, said club head comprisesa hosel, a front and a back defining a cavity, wherein the frontcomprises a hitting zone located opposite to and coinciding with thecavity and wherein the hitting zone has an aspect ratio (AR) defined bythe following equation:AR≧−((1/4.5)×LA)+25,wherein the aspect ratio is defined as the area of the hitting zonedivided by its minimum thickness.

The malleable or forged metal is preferably stainless steel having yieldstrength of less than or equal to 90,000 psi and over about 13% inelongation. More preferably, the material has yield strength of lessthan about 85,000 psi and ultimate elongation of about 15% to about 21%.The forged metal preferably contains more than 10% chromium (Cr).

The iron-type golf club head can be any of the number 1-9 irons, thepitching wedge, the sand wedge and the gap wedge.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a front view of a club head in accordance with an embodimentof the present invention, with the grooves omitted for clarity;

FIG. 2 is a back view of the club head of FIG. 1;

FIG. 3 is an isometric back view of the club head of FIG. 1;

FIG. 4 is a top view of the club head of FIG. 1;

FIG. 5 is a sole view of the club head of FIG. 1;

FIG. 6 is a heel view of the club head of FIG. 1;

FIG. 7 is a toe view of the club head of FIG. 1;

FIG. 8 is an isometric back view of a club head in accordance withanother embodiment of the present invention;

FIGS. 9(a) and 9(b) are magnified photographs of the microstructure of aforged material suitable for use in the club heads of the presentinvention;

FIGS. 10(a) and 10(b) are magnified photographs of the microstructure ofthe forged material of FIGS. 9(a) and 9(b) after annealing;

FIG. 11 is a graph showing the cavity volume of the club heads inaccordance with the present invention;

FIG. 12 is a graph showing the areas of the hitting zones of the clubheads in accordance with the present invention;

FIG. 13 is a graph showing the exemplary minimum thickness of thehitting zones of the club heads in accordance with the presentinvention;

FIG. 14 is a graph showing the aspect ratios between the areas of thehitting zones of FIG. 12 and the minimum thickness of FIG. 13; and

FIG. 15 is a cross-sectional view of the club of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Club head 10 in accordance with an embodiment of the present inventionis illustrated in FIGS. 1-7. Club head 10 comprises front 12, back 14,top 16, sole 18, heel 20, toe 22 and hosel 24. The club head is asingle-piece forging, i.e., it is forged from a single ingot and doesnot include a face insert, or it is formed from a stainless steel bodyand stainless steel insert. The body is forged and the face insert isforged or stamped. A shaft (not shown) is connected to the club head athosel 24 and a grip (not shown) is provided at the top end of the shaft.The grooves on the front 12 are omitted from the figures for clarity.Front 12 comprises hitting zone 26, which preferably is defined by therear cavity area and is located opposite to top portion 28 andreinforced portion 30 as best illustrated in FIGS. 2 and 3. Club head 10is a “cavity back” club, i.e., a substantial portion of the mass of theclub head is positioned on the back side around perimeter 32 of the clubhead. As explained further below, the cavity back design provides theclub with larger rotational moments of inertia to resist the club'stendency to rotate caused by off-center hits. Inside perimeter 32, topportion 28 is the thinnest member of hitting zone 26. The minimumthickness of front 12 is in top portion 28. Reinforced portion 30 isthicker than top portion 28 to provide some structural support to thehitting face. Taken together, top portion 28 and reinforced portion 30resemble a traditional “muscle-back” forged club. Club head 10 also hasa distinctive appearance of having a muscle-back within a cavity back.Reinforced portion 30 may have depressions 34 to provide the club withmore distinctiveness.

Additionally, the mass distribution within perimeter 32 is biased towardsole 18, so that the center of gravity of club head 10 is both behindand below the geometric center of the face. The geometric center can bedefined as the intersection of a vertical centerline and a horizontalcenterline of front 12, or it can be defined as the midpoint of thegrooves. As best illustrated in FIGS. 3, 4 and 7, the thickness at thetop of perimeter 32 is substantially thinner than the thickness at thebottom of perimeter 32. When the center of gravity is below and behindthe geometric center of the hitting face, the club can launch the golfball to higher trajectory and longer flight distance.

Another embodiment of the present invention is illustrated in FIG. 8.This embodiment is substantially similar to the embodiment of FIGS. 1-7,except that this club head is an “oversize” club head. As used herein,oversize club head includes, but is not limited to, club heads that aredimensionally larger than the traditional club heads, club heads thathave larger “sweet-spots” than traditional club heads, and cavity backclub heads that have a relatively higher cavity volume. Cavity volume isdefined as the volume within a three-dimensional shape bounded by thesurface of the back of hitting zone 26, i.e., the combined surfaces ofportions 28 and 30, the inner surface of perimeter weight 32 and animaginary planar or curvilinear plane formed by outer edge 36 ofperimeter 32. Outer edge 36 is best illustrated in FIG. 7. The club headof FIG. 8 is the oversize version of the club head of FIGS. 1-7, becauseof the relative difference in cavity volumes. This cavity volumedifference is best illustrated by the relative difference in thickness38 of perimeter 32 shown in FIG. 3 and in FIG. 8. FIG. 15 illustrates across-sectional view of this club showing minimum thickness t₁ of topportion 28 and thickness t₂ of reinforced portion 30.

The table below shows the preferred cavity volumes for the clubs inaccordance with the present invention: Inventive Clubs InventiveOversize Clubs Club Cavity Volume Cavity Volume Type Loft° (cm³) Loft°(cm³) 1 17.5 12.36 2 19.5 11.58 19.0 14.1 3 22.0 11.75 21.5 13.62 4 25.010.78 24.0 13.35 5 28.0 10.45 27.0 13.31 6 31.0 10.64 30.0 13.05 7 35.08.68 34.0 13.18 8 39.0 8.92 38.0 13.24 9 43.0 9.10 42.0 13.05 PW 47.09.09 46.0 13.37 SW 51.0 8.96 50.0 13.66The cavity volumes for these two embodiments of club head 10 are plottedin FIG. 11 as a function of the loft angle of the club head. As depictedin FIGS. 11, 13 and 14, curve A depicts the characteristics of theinventive clubs and curve B depicts the characteristics of the inventiveoversize clubs. FIG. 11 readily shows that the cavity volume for theoversize clubs is always larger than the cavity volume for the otherclubs. Furthermore, for clubs with loft angle (LA) less than about 32°,the cavity volume is greater than about 10 cm³ (cc). The cavity volumeis at least about 8 cc for all clubs. For the oversize clubs, the cavityvolume is at least about 12 cc for all clubs, and preferably the cavityvolume is greater than about 13 cc. Additionally, as discussed below,the larger cavity volumes of the inventive oversize clubs produce thedesirable high rotational moment of inertia.

In accordance with one aspect of the present invention, malleablestainless steel is a preferred material for the forging process.Typically carbon steel had been used for forging due to its softness.However, because carbon steel rusts, the club head is chrome plated forprotection. Chrome plating is not ductile and thus subject to cracking.This limits the lie, loft and bending ability of the club head. Chromeplating also limits the ability of golf club manufacturers to grind thefinished head to customize weight, shape and/or sole configuration,since the thin chrome plating would be eliminated.

Preferred stainless steels have yield strength of less than about 90,000psi and over about 13% in elongation. More preferably, the material hasyield strength of less than about 85,000 psi and ultimate elongation ofabout 15% to about 21%. Preferred stainless steels also have a RockwellHardness of less than about 25 HRC (Hardness Rockwell C scale). Suitablestainless steels include the 410 stainless steel, which has thefollowing chemical composition: 86.98% Fe, 11.3% Cr, 0.723% Mn, 0.366%Si, 0.297% Ni, 0.11% C, 0.034% P, 0.033% Cu, 0.03% Mo, 0.02% V, 0.017%S, and 0.01% Al. Another suitable stainless steel is the 403 stainlesssteel, which has the following chemical composition: 86% Fe, 12.3% Cr,max 1% Mn, max 0.5% Si, max 0.15% C, max 0.04% P and max 0.03% S.

A forged club head made from 410 stainless steel has a hardness in therange of about 14.2 to about 17.3 HRC. The forging process may comprisemultiple forging steps, wherein each forging step is followed by otherprocessing steps such as grinding, sandblasting, removing flash, andtrimming, among others. For example, the forging process may have aprimer forging step followed by grinding and/or sandblasting beforemultiple rough forging steps are carried out. More grinding andsandblasting can occur before the grooves are cut or stamped and fineforging steps are performed to finish the forging process.

In accordance with another aspect of the present invention, the forgedclub head is further treated by annealing (heating) to decrease itshardness to less than about 40 HRC and preferably less than about 90HRB, more preferably about 80 HRB. In one embodiment, the hardness isannealed to between 20-40 HRC for durability. In a preferred embodiment,the club is made softer for customization and has a hardness less thanabout 90 HRB. In one example, the forged club head is heated to about1050° C. for about 90 minutes and then to about 650° C. for about 120minutes.

The post-forging heat treatment brings the hardness of the forged clubhead to any desired hardness. Advantageously, the increased hardnessresolves the problem of the forged club head being too hard and beingeasily customized in loft and lie. The hardness of the annealed forgedmaterial is also advantageously in the same range as the hardness of thecast materials, e.g., cast 431 stainless steel or cast 8620 carbonsteel, used in the high-end cast clubs, such as Titleist® DCI irons. Thephysical properties of these materials are shown below: Tensile TensileStrength Strength Material Density Hardness (Ultimate) (Yield)Elongation 410 SS (forged 7.72 g/cm 24 HRC-77  97,000 psi 70,000 psi 16%& annealed HRB 403 SS (forged (same as 410 SS) & annealed) 416 SS 7.6421 HRC 107,000 81,900 20% (machined) 431 SS (cast) 7.67 20-28 HRC 95,000 60,000 18% S20C (forged) 7.87 85-95 HRB  80,000 55,000 20% 8620(cast) 7.75 85-90 HRB  85,000 60,000 20%Hence, the present invention resolved the thick hitting face problem offorged irons by selecting a ductile or malleable forgeable stainlesssteel that is better than chrome-plated soft carbon steel and annealingthe forged club head.

Another advantage realized by the annealing step is that the crystallinestructure of the forged material improved. As illustrated in FIGS. 9(a)and 9(b), the microstructure of the forged club head comprisesrelatively small grain size, and as shown in FIGS. 10(a) and 10(b) thegrain size has significantly increased. Metals with larger grain sizemicrostructure have higher ductility. Preferably, the grain size isgreater than about 10 μM to about 50 μm. As shown in the above table,the ductility of annealed and forged 410 SS has elongation propertiesapproaching that of cast 431 SS. The chemical composition for 431stainless steel is 82% Fe, 15-17% Cr, 1.25%-2.5% Ni, max 1% Mn, max 1%Si, max 0.2% C, max 0.04% P and max 0.03% S.

Additionally, the bending ability of forged and annealed 410 SSsurpassed 17-4 PH SS, another commonly used metal for iron-type clubsand similar to cast 431 SS. Other suitable materials include, but arenot limited to, forgeable 403 SS, 431 SS, 416 SS, 303 SS, 304 SS, 329SS, 316 SS, 259 SS, Nitronic 40, Nitronic 50 and Nitronic 60. Suitablestainless steels have at least 10% Cr. The forging and annealingprocesses can readily be adjusted to reach the desirable hardness,tensile strength and ductility in accordance with the process describedabove.

The inventive iron-type clubs can have a hitting zone minimum thicknessin the same range as the thickness of cast iron-type clubs. In oneembodiment, the thickness of hitting zone 26 can be less than about0.100 inch. The inventors of the present invention have produced clubswith a hitting zone as thin as about 0.098 inch for the long irons,i.e., the no. 1, 2 and 3 irons. In other embodiments, particularly inthe two-piece embodiment, i.e., a forged body and a forged or stampedinsert, the thickness can be as low as 0.060 inch.

The minimum thickness of hitting zone 26 can be characterized in termsof the clubs' aspect ratio, which is the ratio of hitting zone 26 overits minimum thickness. Referring to FIG. 2, the area of hitting zone 26within front 12 is estimated as the product of the length L of hittingzone 26 and the average height of hitting zone 26. Two representativeheights, H₁ and H₂, are illustrated. In other words, hitting zone 26 isthe area within front 12 opposite to and coinciding with top portion 28and reinforced portion 30 of the cavity back. The minimum thickness t₁is measured within top portion 28. The defined aspect ratio covershitting zone 26, where the area of top portion 28 makes up from about50% to about 90%, more preferably from about 60% to about 80%, of thetotal area of hitting zone 26. The thickness of reinforced portion 30can be about 1.2 times to about 3 times the thickness of top portion 28.The relative thickness between top portion 28, t₁, and reinforcedportion 30, t₂, is illustrated in FIG. 15. Inventive Clubs Face Area ofHitting Club Front 12 Zone 26 Thickness Aspect Ratio Type Loft° (inch²)(inch²) (inch) (inch) 1 17.5 4.165 2.548 0.110 23.16 2 19.5 4.185 2.5030.110 22.75 3 22.0 4.202 2.538 0.110 23.07 4 25.0 4.231 2.373 0.11520.63 5 28.0 4.216 2.330 0.120 19.42 6 31.0 4.317 2.338 0.125 18.70 735.0 4.379 2.240 0.130 17.23 8 39.0 4.545 2.346 0.135 17.38 9 43.0 4.6602.323 0.140 16.59 PW 47.0 4.755 2.345 0.145 16.17 SW 51.0 4.800 2.2770.150 15.18

Inventive Oversize Clubs Face Area of Hitting Club Front 12 Zone 26Thickness Aspect Ratio Type Loft° (inch²) (inch²) (inch) (inch) 2 19.04.258 2.506 0.110 22.78 3 21.5 4.322 2.363 0.110 21.48 4 24.0 4.3042.421 0.115 21.05 5 27.0 4.383 2.466 0.120 20.55 6 30.0 4.391 2.3770.125 19.02 7 34.0 4.476 2.377 0.130 18.28 8 38.0 4.644 2.471 0.13518.30 9 42.0 4.750 2.498 0.140 17.84 PW 46.0 4.864 2.528 0.145 17.43 SW50.0 4.920 2.535 0.150 16.90

As used herein, club nos. 1-9, pitching wedge (PW) and sand wedge (SW)have common accepted descriptions used in the golf club art. A set ofirons typically includes clubs ranging from 3-iron to PW or 5-iron to PWwith other clubs being available for custom orders. It is also notedthat a manufacturer can make different clubs within a set in differentmanners, such as cavity back/muscle back sets. Iron-type clubs may alsoinclude a gap wedge. These clubs can also be described by othervariables including, but not limited to, the loft angle. The areas ofhitting zone 26 are plotted in FIG. 12, the minimum thicknesses of topportion 28 are plotted in FIG. 13 and the aspect ratios between theareas of hitting zone 26 and minimum thickness are plotted in FIG. 14.In FIGS. 12 and 14, Curves A illustrate the areas of hitting zone 26 andthe aspect ratios for the inventive clubs and Curves B illustrate theareas of hitting zone 26 and aspect ratios for the inventive oversizeclubs.

FIG. 12 illustrates large hitting zones for the inventive clubs and forthe inventive oversize clubs, which are the results of having large faceareas combined with large cavity volumes. FIG. 13 illustrates the thinsingle-piece stainless steel forged face having a minimum thickness ofless than or equal to about 0.200 inch, and preferably the less thanabout 0.130 inch for clubs with LA of less than about 35°. FIG. 14 showsthe aspect ratios (AR) of the clubs of the present invention, and theadvantages of having a large hitting area and a thin face. The AR can beexpressed asAR≧−((1/4.5)×LA)+25.Curve C is the linear line representing this equation in FIG. 14.

Rotational moment of inertia (“inertia”) in golf clubs is well known inart, and is fully discussed in many references, including U.S. Pat. No.4,420,156, which is incorporated herein by reference in its entirety.When the inertia is too low, the club head tends to rotate excessivelyfrom off-center hits. Higher inertia indicates higher rotational massand less rotation from off-center hits, thereby allowing off-center hitsto fly farther and closer to the intended path. Inertia is measuredabout a vertical axis going through the center of gravity of the clubhead (I_(yy)), and about a horizontal axis about the center of gravity(c.g.) of the club head (I_(xx)), as shown in FIG. 1. The tendency ofthe club head to rotate around the y-axis through the c.g. indicates theamount of rotation that an off-center hit away from the y-axis causes.Similarly, the tendency of the club head to rotate in the around thex-axis through the c.g. indicates the amount of rotation that anoff-center hit away from the x-axis through the c.g. causes. Mostoff-center hits cause a tendency to rotate around both x and y axes.High I_(xx) and I_(yy) reduce the tendency to rotate and provide moreforgiveness to off-center hits.

Inertia is also measured about the shaft axis (I_(sa)), shown in FIG. 1.First, the face of the club is set in the address position, then theface is squared and the loft angle and the lie angle are set beforemeasurements are taken. Any golf ball hit has a tendency to cause theclub head to rotate around the shaft axis. An off-center hit toward thetoe would produce the highest tendency to rotate about the shaft axis,and an off-center hit toward the heel causes the lowest. High I_(sa)reduces the tendency to rotate and provides more control of the hittingface. High I_(xx), I_(yy) and I_(sa) have been achieved in high-end castiron-type clubs. This can now be realized in high-end forged iron-typeclubs in accordance with the present invention.

As discussed above, the hitting zone of the club head can be as thin asabout 0.100 inch for a 2-iron and about 0.150 inch for a sand wedge(SW). The weight is moved to the perimeter of the club head, and thesole can be as thick as about 0.540 inch to about 0.780 inch and the topcan be as thick as about 0.180 inch to about 0.380 inch, preferablyabout 0.240 inch to about 0.320 inch. Exemplary inertias of theinventive clubs calculated by computer aided design (CAD) are shownbelow and compared to the inertia of a traditional forged muscle back(with no perimeter weighting). The comparative clubs are the Titleist®670 Forged Irons. CAD-generated Inventive Oversize Clubs Inventive ClubsComparative Clubs Club type 3 6 9 3 6 9 3 6 9 I-xx (kg-mm²) 52.7 56.570.0 50.5 55.7 70.7 47.3 54.6 72.8 I-yy 234.8 244.8 270.3 228.0 240.5264.7 189.3 202.4 238.9 I-sa 526.6 595.2 662.5 472.2 536.7 608.6 389.4435.3 488.3 CG-y (mm) 18.6 18.5 18.7 18.3 18.4 18.7 19.6 19.7 19.6 CG-sa37.8 37.6 37.6 34.8 35.8 36.1 32.1 32.2 31.6 weight (kg) 0.243 0.2610.283 0.241 0.260 0.282 0.240 0.259 0.281* data created from CAD files.

As discussed above, the relative large cavity volumes of the inventiveoversize clubs produce high rotational moments of inertia, particularlyI_(sa) and I_(yy).

The locations of the center of gravity are also listed above. GC-y ismeasure from the ground when the club rests in the address position;CG-x is measured from the center of the face in the same position; andCG-sa is measured from the shaft axis in the same position. The centerof gravity is located behind and below the geometric center of hittingface. The geometric center can be defined as the midpoint of the groovesor score lines, as stated above. It is readily apparent that the momentsof inertia of the inventive clubs are higher than the moments of inertiaof the comparative clubs.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives stated above, it is appreciatedthat numerous modifications and other embodiments may be devised bythose skilled in the art. Therefore, it will be understood that theappended claims are intended to cover all such modifications andembodiments, which would come within the spirit and scope of the presentinvention.

1. An iron-type golf club comprising: a club head having a hosel, afront and a back, wherein the back comprises a cavity defined by aperimeter member and the front has a hitting zone located opposite toand coinciding with the cavity, and wherein the club head is forged fromstainless steel and then annealed, wherein the cavity volume is greaterthan or equal to 8.68 cc.
 2. The iron-type golf club of claim 1, whereinthe cavity is further adjoined by a first portion and a reinforcedportion located on the back of the club head and wherein the reinforcedportion is thicker than the first portion.
 3. The iron-type golf club ofclaim 2, wherein the first portion is located on top of the reinforcedportion.
 4. The iron-type golf club of claim 2, wherein the thickness ofthe reinforced portion is about 1.2 times to about 3 times higher thanthe thickness of the first portion.
 5. The iron-type golf club of claim2, wherein the first portion occupies from about 50% to about 90% of thetotal area of the hitting zone.
 6. The iron-type golf club of claim 5,wherein the first portion occupies from about 60% to about 80% of thetotal area of the hitting zone.
 7. The iron-type golf club of claim 1,wherein the perimeter member is thicker on the bottom of the club headthan on the top.
 8. The iron-type golf club of claim 1, wherein thestainless steel has a yield strength less than about 90,000 psi and anelongation of greater than about 13%.
 9. The iron-type golf club ofclaim 8, wherein the yield strength is less than about 85,000 psi andthe stainless steel has an ultimate elongation of about 15% to about21%.
 10. The iron-type golf club of claim 1, wherein the stainless steelcomprises more than about 10% of chromium.
 11. The iron-type golf clubof claim 1, wherein the grain size of the forged and annealed stainlesssteel is greater than about 10 μm.
 12. The iron-type golf club of claim11, wherein the grain size of the forged and annealed stainless steel isbetween about 10 μm and about 50 μm.
 13. The iron-type golf club ofclaim 1, wherein the club head is a unitary club head.
 14. The iron-typegolf club of claim 1, wherein the club head further comprises a forgedface insert, and wherein the face insert is made from stainless steel.15. The iron-type golf club of claim 1, wherein the club head furthercomprises a stamped face insert and wherein the face insert is made fromthe stainless steel.
 16. The iron-type golf club of claim 1, wherein theclub head has a hardness of less than about 90 Rockwell Hardness B. 17.The iron-type golf club of claim 1, wherein the stainless steel isselected from a group consisting of 410 stainless steel, 403 stainlesssteel, 431 stainless steel, 416 stainless steel, 303 stainless steel,304 stainless steel, 329 stainless steel, 316 stainless steel, 259stainless steel, Nitronic 40, Nitronic 50 and Nitronic
 60. 18. Theiron-type golf club of claim 1, wherein the club head is selected from agroup consisting of the number 1-9 irons, the pitching wedge, the sandwedge and the gap wedge.
 19. The iron-type golf club of claim 1, whereinthe rotational moment of inertia about a shaft axis is greater thanabout 500 kg·mm².
 20. The iron-type golf club of claim 19, wherein therotational moment of inertia about the shaft axis is greater than about650 kg·mm².
 21. The iron-type golf club of claim 1, wherein the hittingzone has a minimum thickness of less than about 0.2 inch.
 22. Theiron-type golf club of claim 21, wherein the minimum thickness is lessthan about 0.13 inch when the loft angle is less than about 35°.
 23. Theiron-type golf club of claim 21, wherein the minimum thickness is about0.1 inch.
 24. The iron-type golf club of claim 1, wherein the hittingzone has an aspect ratio in accordance to the following equation:aspect ratio≧−((1/4.5)×loft angle°)+25, wherein the aspect ratio is thearea of the hitting zone (inch²) divided by a minimum thickness (inch)of the hitting zone.
 25. An iron-type golf club comprising: a club headhaving a hosel, a front and a back, wherein the back comprises a cavitydefined by a perimeter member and the front has a hitting zone locatedopposite to and coinciding with the cavity, and wherein the club head isforged from stainless steel and then annealed, wherein the cavity volumeis greater than or equal to 13.05 cc.